Hi! Yes, "idioma" and "lengua" are normally interchangeable and used in similar contexts or expressions. There exist just some few differences between them: both words are used to refer to modern languages (as in your example: "idioma español" and "lengua española" mean the same), but "idioma" is not used to speak about dead languages, like latin (in spanish "lengua latina", never "idioma latino"). Regards:)

In theory, they mean the same thing and can be used interchangeably, but in practice, this is not usually the case. I rarely use "lengua", in fact, I usually just saw it in text books. But in an informal context (at least in my country), it was almost never used. For example, people would say "hablo 3 idiomas" (I speak 3 languages) instead of "hablo 3 lenguas" (I speak 3 tongues), it would technically be correct but it just doesn't sound very natural. It's basically the same as in English, how we can say "native language" or "mother tongue" (after all, lengua literally means tongue).

Well, "idioma" and "lengua" are freely interchangeable, but ... In Spain, we use "idioma" (and can use lengua) In south american hispanic countries they use "lengua" the most, but "idioma" too.

They are the same but lengua is almost never used. It is common to use the word Idioma to refer to any language in the world.

2个都是语言 但是idioma就是语言的意思，比较书面 lengua本来的意思其实是舌头，引申为语言了